Electric utilities or distribution organizations, hereafter referred to as electricity suppliers, are responsible for supplying an economic, reliable and safe source of electricity to customers. The electricity supplier, through its' energy delivery system, provides electricity to its customers at a suitable voltage and frequency. This electricity is provided on an instantaneous basis. That is, when the customer turns on an appliance, the electricity supplier provides the electricity to the customer's appliance the instant that the customer flips the switch on.
One well-known difficulty in providing electricity to customers is precisely matching the total amount of electricity consumed by all of the customers on an instantaneous basis with the amount of electricity generated and/or purchased by the electricity supplier. The total amount of electricity used at any given instant in time is commonly referred to as demand. Demand typically is measured in units of watts, kilo-watts (KW), or mega-watts (MW). For example, a conventional light bulb may have a demand of 100 watts. Ten (10) of these light bulbs has a demand of 1 KW. If one thousand of these light bulbs are all turned on at the same instant in time, the electricity supplier must instantly provide an additional 100 KW of electricity by increasing generation and/or purchases.
Most changes in demand, either up or down, are a small percentage of the overall delivery system load and result in little, if any, mismatch between supply and demand. This minor mismatch rarely causes a measurable change in system voltage or frequency. Significant mismatches between demand and supply occur when either the delivery system or supply (generation and/or purchases) cannot meet demand. As this mismatch increases, a voltage drop starts to occur. When significant mismatches between demand and supply occur, distortion in the electric system frequency occurs.
Currently there are devices designed to automatically remove loads when either voltage or frequency are out of tolerance, both at the appliance and system level.
U.S. Pat. No. 6,541,740 entitled “Heater/Blower Unit With Load Control” which issued on Apr. 1, 2003 to Ziaimehr et al. uses a two-heater system with a method of minimizing fluctuations in the load on a high wattage electrical device.
U.S. Pat. No. 6,671,586 entitled “System and Method for Controlling Power Demand over an Integrated Wireless Network” which issued on Dec. 30, 2003 to Davis et al. discloses an intelligent network demand control system which employs a transceiver network coupled to meters and appliances.
U.S. Pat. No. 6,836,737 entitled “Systems and Methods for Providing Remote Monitoring of Consumption for a Utility Meter” which issued on Dec. 28, 2004 to Petite et al. discloses a plurality of electric meters and communications devices which define a wireless communications network for controlling the consumption of electric power.
U.S. Pat. No. 6,862,498 entitled “System and Method for Controlling Power Demand over an Integrated Wireless Network” which issued on Mar. 1, 2005 to Davis et al. provides an intelligent demand control system for an energy delivery system using a wireless transceiver network for reducing energy demand as needed.
As another example, if the electricity supplier loses a generator in an unplanned manner, the electric system demand will exceed supply. If the mismatch is sufficiently large, the electric frequency will drop from its nominal value of 60 hertz (Hz), in the United States. If the frequency drops to below 59.8 Hz, relays sense the frequency decay and operate to selectively disconnect predefined groups of customers from the energy delivery system. Demand is reduced, hopefully to the point where demand again approximately equals supply such that the frequency recovers back to its nominal 60 Hz value. Disconnecting customer loads to arrest frequency decay is known as load shedding.
Although the action of the frequency sensitive relays effectively arrests the undesirable frequency decay, thereby saving the energy delivery system from a more severe decay in frequency and other undesirable associated problems, those customers that were disconnected did not volunteer to be selected as participants in the load-shedding scheme. Furthermore, the electricity supplier loses the associated sales to the affected customers, thereby negatively impacting the electricity supplier's revenue stream.
One well-known technique to decrease the frequency of occurrence of these undesirable mismatches between energy demand and supply is to couple selected energy consuming loads to radio frequency (RF) controlled receivers. Then, when a mismatch in demand and supply occurs, or when the electricity supplier anticipates that a mismatch occurrence is eminent, the electricity supplier orders the shut off of the selected energy consuming loads by transmitting a shut-off signal to the RF receivers. Such a group of aggregated loads is commonly referred to as a load block. Participation in such a load block is typically voluntary. Often, customers are offered incentives to participate. For example, a customer can be given a decrease in rate and/or a rebate to voluntarily allow the electricity supplier to couple an RF receiver to their load.
The previous example is based upon mismatches when supply (generation and/or purchases) does not match demand. Mismatches occurring due to the delivery system inadequacies are something that the electricity supplier cannot easily monitor or correct. A local customer premises transformer can be overloaded due to concurrent demands from each of the residences. Also a transformer that is feeding a plurality of customer premises transformers can become overloaded without affecting the majority of the delivery system. These types of problems are very expensive for an electricity supplier to remedy, as it involves major changes to the delivery system.
With all of these methodologies, the electricity supplier is still faced with the peak demands that are placed on the energy delivery system everyday. Many electricity suppliers offer rate structures that provide an incentive to utilize power during typical ‘off-peak’ times. This approach may limit demand peaks during one time frame, however it most often causes another. Electricity suppliers can increase generating capacity and/or purchase additional power to support these peak demands. Either approach means that the cost of the electricity is more than during normal operation, thereby negatively impacting the electricity supplier's revenue stream.
Yet another problem that the electricity supplier faces is the power factor issue that occurs due to HVAC units (or any significant motor load). Some electricity suppliers utilize constant voltage transformers (CVT) to help offset power factor influences. Another philosophy is to switch large banks of capacitors in or out of a circuit as necessary. This is not typically an approach that can be used to correct a power factor issue quickly, as personnel must be sent out to switch these banks. Most implementations of capacitor bank switching is done on a seasonal basis, due to anticipated motor loads. Some electricity suppliers have implemented capacitor bank switching at the substation level and do so without requiring personnel to be sent out. This still does little to affect the more local overloading that occurs due to power factor influences.
Thus, a need exists in the industry for providing a demand limiting and control system that accurately monitors the supplied electricity and intelligently determines the need for load shedding, in real time. Also, there is a need in the industry to provide a system that allows for selective determination of the best combination of loads to meet the desired reduction. There is also a need to allow the customer to determine what load(s) is available for shut-off. And finally a need in the industry is to control power factor throughout the energy delivery system such that energy losses due to overheating of components is reduced to a minimum.
The present invention meets these needs.